Researchers have taken yet another step toward creating super-tiny circuits using nanotubesthose miniature straws of pure carbon that can conduct electricity, mimic transistors, act as quantum wires and perform a number of other neat electrical tricks. Florian Banhart of the University of Ulm in Germany actually managed to solder together two carbon nanotubes, measuring just two millionths of a millimeter across. He describes his accomplishment in the current issue of the journal Nano Letters.
Banhart couldn't join the nanotubes just any old way. Because of their size, two carbon nanotubes in contact will not, like ordinary wires, conduct electricity very well. So Banhart used a kind of substitute soldercreated on the spotto link two crossed nanotubes: he focused a narrow beam of electrons from a scanning electron microscope at the point where the tubes met, thereby converting contaminants on their surfaces into bridges made from graphite-like carbon that can conduct electricity. "To conclude," Banhart writes, "a connection between carbon nanotubes was achieved by depositing carbon contamination selectively at nanotube junctions with an electron beam." High-resolution images from a transmission electron microscope confirmed the connection. Now scientists will have to probe the electrical properties of these nanotube junctions.